1. Field of the Invention
The present invention relates to integrated circuit packages, and more specifically, to the production of a chip scale integrated circuit package using a lead frame.
2. Related Art
An integrated circuit (IC) package encapsulates an IC chip, or die, in a protective casing and also provides power and signal distribution between the IC chip and an external printed circuit board (PCB). A common IC package uses a metal lead frame to provide the electrical paths for that distribution. For production purposes, a lead frame panel 110 made up of multiple lead frames 120 is etched or stamped from a thin sheet of metal, as shown in FIG. 1a. An IC chip 130 is then mounted and wire bonded to each lead frame 120, as shown in FIG. 1b. Wire bonding is typically performed using fine gold wires 140. Each IC chip 130 is then encapsulated in a protective casing 160, which can be produced by installing a preformed plastic or ceramic housing around each IC chip 130, or by dispensing and molding a layer of encapsulant material over all IC chips 130. Next, lead frames 120 are cut apart, or singulated, and multiple electrical interconnections are attached to the lead frame in order to produce individual IC packages 190, as shown in FIG. 1c. The electrical interconnections provide the electrical interface between IC package 190 and the external PCB, and can take a variety of forms. FIG. 1c depicts a lead frame ball grid array (BGA) IC package in which electrical interconnections are provided by solder balls 150 mounted on the bottom surface of lead frame 120. Other types of electrical interconnections can be seen in FIG. 1d, which shows examples of common IC packages using lead frames, including a small outline package (SOP) 191, a pin-through-hole (PTH) package 192, and a plastic leaded chip carrier (PLCC) 193.
The use of a lead frame provides an inexpensive means for IC package manufacturing. Etching or stamping a sheet of thin metal to produce the desired lead frame patterns is a well-known manufacturing process, and is conducive to high-volume, low-cost production. In addition, the lead frame panel provides a support framework for the IC chips during IC package assembly. However, as IC chip device densities increase and IC package sizes decrease, the geometries used in the electrical communication paths between the IC chip and the PCB decrease. For example, a chip scale package requires that the protective casing be no more than 20% larger than the IC chip. As a result, the area available for the electrical paths provided by the lead frame is significantly reduced, demanding much finer lead frame patterns. In order to construct that finer geometry, the lead frame thickness must be reduced to a point where the lead frame panel rigidity would no longer be sufficient to provide the necessary support during the IC package assembly process. Also, the fragile lead frame patterns would be more susceptible to damage during the manufacturing process. As a result, chip scale IC packages must use more costly techniques such as tape automated bonding (TAB) or printed substrate backing.
Accordingly, it is desirable to provide an IC packaging method that allows the use of a lead frame in a chip scale package.